This invention relates to control of an intake air amount of an engine provided with a turbocharger.
Tokkai Hei 8-338256 published by the Japanese Patent Office published in 1996 discloses a feedback control of a supercharging pressure variation mechanism of a turbocharger of an engine based on a target value.
This prior art technique detects a supercharging pressure or an intake air amount of the engine, and operates the supercharging pressure variation mechanism so that the detected value coincides with a target value that was determined according to the running condition of the engine.
The turbocharger comprises an exhaust gas turbine disposed in an exhaust passage of an engine, and a compressor driven by the exhaust gas turbine which compresses air, and supplies it to an intake passage of the engine.
The supercharging pressure variation mechanism comprises for example a gate which varies an inflow cross-sectional area of exhaust gas to the exhaust gas turbine.
Such feedback control also compensates scatter in the performance of sensors which detect the supercharging pressure or intake air amount, and the performance of an actuator which operates the supercharging pressure variation mechanism. However, there is a considerable response delay in a process wherein the gate operation of the exhaust gas turbine affects the intake air amount of the engine.
This response delay is specified by a response time until the intake air amount starts to change after the gate operation, and a time constant representing the variation rate of the intake air amount.
The response time is several hundreds milliseconds and the time constant is in units of several seconds.
If the intake air amount is set as a target value and feedback control of the gate opening is performed by the well-known differential/integral feedback control, the following problem will arise due to this response delay.
When the intake air amount changes in a stepwise manner, an integral correction value in feedback control accumulates due to the response delay in the real fresh air amount.
This accumulation of the integral correction value affects the opening command value of the gate, and causes the intake air amount to oscillate around the target value. In an engine which performs exhaust recirculation (EGR) which returns part of the exhaust gas to the intake air, oscillation of the intake air amount leads to an impairment of the exhaust gas composition of the engine.
It is therefore an object of this invention to suppress oscillation of the intake air amount of the engine resulting from operation of a supercharging pressure variation mechanism.
In order to achieve the above objects, this invention provides a control device for a turbocharger of an engine, wherein the turbocharger is provided with an exhaust gas turbine driven by an exhaust gas of the engine, a compressor which supplies fresh air to the engine under a supercharging pressure according to a rotation of the exhaust gas turbine, and a mechanism which adjusts a flowpath cross-sectional area of the exhaust gas led to the exhaust gas turbine. The control device comprises a sensor which detects a running state of the engine, a sensor which detects an intake air amount of the engine, and a controller. The controller is functioning to set an open loop control value of the flowpath cross-sectional area based on the running state, set a target intake air amount of the engine based on the running state, calculate a processing value wherein predetermined smoothing is performed on the target intake air amount, calculate a feedback correction amount which makes the intake air amount coincide with the processing value, and control the exhaust gas flowpath cross-sectional area of the mechanism based on the open loop control value and feedback correction amount.
This invention also provides a control method of a turbocharger of an engine, wherein the turbocharger is provided with an exhaust gas turbine driven by an exhaust gas of the engine, a compressor which supplies fresh air to the engine under a supercharging pressure according to a rotation of the exhaust gas turbine, and a mechanism which adjusts a flowpath cross-sectional area of the exhaust gas led to the exhaust gas turbine. The control method comprising detecting a running state of the engine, detecting an intake air amount of the engine, setting an open loop control value of the flowpath cross-sectional area based on the running state, set a target intake air amount of the engine based on the running state, calculating a processing value wherein predetermined smoothing is performed on the target intake air amount, calculating a feedback correction amount which makes the intake air amount coincide with the processing value, and controlling the exhaust gas flowpath cross-sectional area of the mechanism based on the open loop control value and feedback correction amount.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.